Process for the manufacture of carbonic-acid gas.



FIG. 1

A. E. KNOWLES.

PROCESS FOR THRMANUFAGTURE 0F GARBONIG AGID GAS. nrmonmn IILED J ULY so, 1907..

Patented July 5, 1910.

2 SHEETS-SHEET 1.

WITNESSES; A

INV E. NTSPR. ALBERT EDGAR KNOWLES VQMS MM LM Attovness.

A. E. KNOWLES. PROCESS FOR THE MANUFAOTURE or GARBONIO ACID GAS.

APPLICATION FILED JULY 30, 1907. 963,586 Patented July 5, 1910.

2-SHEET88HEBT 2.

FIG. 5

WITN E5555: INVENT'QR,

VOJSMIAfiW I I I Afitornegs.

ALBERT EDGAR KNOWLES.

ALBERT EDGAR KNOWLES, OF SUTTON COLDFIELD, ENGLAND.

rnoonss ron TH MANUFACTURE or CARBONVIC-ACID ens.

Specification of Letters Patent.

Application filed July 30, 1907. Serial No. 386,252.

To all whom it may concern:

Be it known that I, ALBERT EDGAR KNOWLES, a subject of the King of Great Britain, and residing at Gable End, Anchorage Road, Sutton Coldfield, in the county of Vvarwi'ck, England, chemical engineer, have invented certain new and useful Improvements in Processes for the Manufacture of Carbonic-Acid Gas, of which the following is a specification.

My invention relates to a process for the manufacture of carbonic acid gas and has for its object the effecting of considerable economy in manufacture product of the best quality.

The process most generally used at-present isbased on the well known property of an alkaline liquid, or lye (or ley)by which is meant, hereinafter, an aqueous solution of potassium or sodium carbonatesof absorbing carbon dioxid at normal temperawhile giving a tures and giving it off again on boiling, the

lye being ready for absorption of the dioxid again after cooling. The combustion of fuelsay coke-is effected to give the'carbon dioxid and the heat generated by this combustion is largely in excess of that required for the decomposition of the bicarbonated lye, so that only the amount of fuel necessaryto give the required weight of CO should be required. In practice considerably more than the theoretical amount of fuel is of course used, and it is in this direction that economy has been sought but use shows that the economy of fuel may be obtained at the sacrifice of the purity of the product or by greatly increased'maintenance charges.

The most successful works have been those in which the product is maintained at a very high state of purity (particularly without any trace of smell caused by the presence of sulfuretedhydrogen and other compounds) and where also the plant has been of a very simple nature, thus obviating risk of breakdown and keeping down maintenance charges. Such a plant consists of a boiler or decomposer fired direct with coke and having a fan draft; the fans drawin the products of combustion through suitable washers to remove sulfur, soot, and other impurities and to cool the gases. The gases are then forced up through towers filled with hard coke and in these towers are brought into contact with cold alkaline lye pumped into the towers at the top. In

Patented July 5, 1910.

the passage down the coke columns the lye absorbs carbon dioXid from the gases passing up the columns, and thecarbonated lye is pumped from the bottom of the towers to the boiler. On its way to the boiler the carbonated lye is passed through pre-heaters generally in the form of heat inter-changers comprising a portion where the cold lye is partially heated by the hot lye, leaving the boiler, and a portion where the lye is further heated by the hot gas, carbonic acid and steam coming from the boiler. The carbonated lye is thus at or near the boiling point as it enters the boiler and when in the boiler distillation and decomposition take place under some small pressure above atmospheric pressure. .In the lye circuit coolers are provided to further cool the lye passing from the preheater to the top of the towers; and coolers are provided for the gas as it leaves the lye heaters for completely cooling it down and for condensing the steam it contains. This then is the most successfulform of plant, its economy being due to its simplicity and reliability while giving a thoroughly good product. But at no point is this plant eflicient; the carbonated lye is never saturated in the absorption part of the plant, nor is itcompletely decomposed'in the decomposing portion, the composition -of the gases passing into the absorption towers is not constant and the gases v passing out, through the towers are not nearly completely decarbonated, still containing a large proportion of the original carbon 'dioxid yfinally an immense waste of heat takes place in the washers, in coolin the products of combustion from the boiler in the gas cooler and in the lye coolers, particularly in the gas cooler.

It has been recognized that the richer in carbonic'acid gas and the'more constant are the products of combustion used in the absorbingtowers, the greater the amount absorbed. Also that pressure greatly assists this absorption. Attempts at economy have therefore been ,made in two directions. First, by the production of fuel. gas in some form and by its combustion obtaining a more constant and richer quality of gas. And,

secondly, by the absorption of the carbonic acid gas under higher pressure.v

This latter has been carried out in two ways, first, by the mechanical compression of the gas passing into the absorbing chambers, and secondly, by using the fuel gas in a gas engine, and using the exhaust products at the exhaust pressure or subsequently compressing before passing into the absorbingvessel. As already mentioned, these attempts at economy have introduced or aggravated other difliculties, particularly have they increased maintenance charges, both for wear and laborand what is more serious have affected the quality of the product. These results have been due tothe increased complication ofthe plant at the very place where wear and corrosion are the greatest, and the production of intermediate hydro-sulfur and hydro-carbon compounds, impossible to remove from the products of combustion used. In the plant described asgiving good results in good practice, with direct coke fired .boilers such products are practically imposbonic acid gas -is not forced too high. The

sulfur impurity is under these conditions sulfur dioxid which presents no diflioulties in its removal and cannot contaminate the final product, as any not; removed in the washers is combined with the lye due to thepresence of nitric acid, forming a sulfate which will not be decomposed by heat.

In investigating the conditions and methods of manufacture of carbonic acid gas, I have found that in manypoints the known laws governing the operations are ignored by makers and that certain of the conditions ignored are conducive to economy in the mty invention consists in a method of man- "l1 acture embodying and applying certain of these'conditions without complicating the necessary apparatus. The conditions are 1. Combination of the lye and carbonic acid gas is produced either by low temperature or highpressure.

2. Decom osition of carbonated lye is ef-- fected by either high temperature or low pressure.

3. That with any fixed sample of lye'and free carbonic acid gas, there is a-fixed temperature corresponding toa fixed pressure at which no reaction takes place. That this temperature rises rapidly with the pressure giving a curve of neutral points. And that any departure from these fixed figures produces reaction for example, at fixed pressure decomposition occurs above this neutral temperature, and combination below, the neutral temperature, or for a fixed temperature,

' pressure above the'neutral effects combination; below effects decomposition.

4. Thatdecomnosition will continue under the conditions given so lon as the carbonated lye is not completely ecarbonated and absorption illoontinue so long as the carbonated lye is not saturated and there is still carbonic acid gas toabsorb.

sible, particularly if the percentage of car-' production of a satisfactory product, and

5. That the neutral points are not materially affected by the percentage ofcarbonic acid in the solution or of the gases in contact.

6. But that the neutral points are altered altogether if the basic contents of the solution are altered, that is to say, if the solution of the alkali is strengthened or weakened.

7. That a weaker alkali liquid decomposes at lower temperatures or higher pressures and similarly combines at lower temperaturesdand higher pressures than a stronger li ui 8. That the amount of heat required to effect decomposition is constant and is exactly equal to the amount of heat produced during absorption and. is not altered by thetemperature at which the processes are carried out. In fact (although probably not economical) it would be quite possible to carry out the reactions Without using any of the heat from combustion. Of these conditions only the first appears to have met with any recognition from designe'rsof plants and this has led to the employment in some cases of absorption under pressure which viewed from the question of economy is a doubtful improvement.

What appears from experiment to be of the utmost importance is the fact that temperature differences can be reduced or even obviated by the efiecting of the decomposition of the carbonated lye under reduced pressure and this has been completely lost sight of and this I make one of the essential features of my process. In connection with =this I may mention that with. a sufiiciently high vacuum it is possible to decompose the nomical to so work.

also been lost sight of and these I utilize in my process with very great advantage, the taking up of the dioxidin the solution and the win it up again being considerably facilitate .by the strengthening of the solution in the absorption part of the apparatus and the dilution of the solution in the decomposin portion. As this may be very readily e ected without complication a large gain is made.

My process therefor consists, first, in varying the strength of the alkali solution between the decomposingand absorbing portions of the plant, that is effected by a weakwing or dilution of the solution in the decomposer; and, secondly,in the employment of this variation of the strength of the solution in conjunction with a reduction of pressure or a partial vacuum inthe decomposer. Both these features'may be carried out in numbers of ways; as an example, the first carbonated: lye at normal temperature, but :in practice it probably would not be ecoforcing the lye to the boiler may be dispensed with and one pump for drawing the lye from the boiler and forcing it to the top of the towers only used. The boiler would then be on the suction side only of a pump, boiled lye being drawn out and circulated while the carbonated lye would be drawn in by thepartial vacuum created. The gas holder for the carbonic-acid gas could also be dispensed with, the gas being drawn direct by the compressor used for the subsequent llquefaction of the gas in charging the cylinders in which it is commercially handled. The second feature can be effected by utilizing the water of condensation from thegas coolers and make up water, that is, water replacing that boiled out, for the dilution of the alkaline liquid before it goes to the boiler. The amount of this would be varied according to the amount boiled oil with the gas from the boiler.

As is shown by the above laws, it is of great advantage to have the carbonated lye in the boiler for a considerable time without pressure and in designing apparatus to carry out my process I prefer to employ means for effecting this in the decomposing apparatus.

What I effect is a great saving in heat and a large reduction of the waste in unabsorbed carbonic acid gas. It may be that in practice it would not be economical to completely absorb the carbonic acid gas although'the laboratory shows this possible, but such a thing can only be regulated and determined as to which is the best in practice. It must be understood that I do not aim at the lye being completely saturated or decomposed at any point of the apparatus, but at greatly facilitating these to give a better and more economical manufacture.

In order that my invention may be particularly understood and easily carried into practical effect, I have appended hereunto 2 sheets of drawings on which 2- Figure 1. is a diagrammatic View of a common type of plant. Fig. 2. is a similar view showing how this type of plant would be modified to effect my process. Fig. 3. is a suitable decomposing apparatus for giving the best practice of the process.

On the drawings at Fig. 1, 1 is the carbonated lye boiler, 2 the flue gas washers, 3 blowers, and 4 absorption towers. A decarbonated lye tank is represented at 5 and a tank for the carbonated-lye at 6. 7 is a pump for forcing the decarbonated lye from the tank 5 to the towers 4, while 8 is a pump for forcing the carbonatedlye from the tank 6 to the boiler. Heat interchangers and gas coolers are arranged in the way of the gas and the lye; 9 is a heater in which the carbonated lye, on its way to the boiler, is partially heated by the hot decarbonated lye passing from the boiler to the tank 5. 10

from the boiler and is a heater in which the carbonated lye, passing to the boiler, is further heated by the gas leaving the boiler on its way to final gas cooler 11, while 12 is the final lye cooler for the decarbonated lye, after leaving the carbonated lye heater, 10. 13 is a separator for condensed steam, l lis the gas holder, and 15 the path of the water from the separator. In this plant, which is the type before mentioned as being the most generally satisfactory, the boiler is tired direct with coke and the products of combustion pass through the washers 2 to the towers 4. The decarbonated lye from the boiler passes through the carbonated lye heater 9, where it gives up part of its heat to the carbonated lye, on its way to the boiler, then passes to the cooler 12 and thence to the decarbonated lye tank 5. .From the tank 5 the decarbonated lye pumped to-the towers where it meets the gas and absorption takes place. The flue gases not absorbed pass out at the flue 16 while the carbonated lye goes to the tank 6 then to the heaters 9 and 10 and thence to the boiler 1. The carbonic acid gas boiled out of the lye passes to the carbonated lye heater '10 then to the final cooler 11 and through the separator 13 where it is cleared of steam, to the holder 14 from which it is led to the compressor as required.

In the plant as altered to carry out my process the pump 8 for forcing the carbonated lye to the boiler is dispensed with, the pump 7, for drawing the decarbonated lye raising it to the top of the towers,.being used alone. The boiler is on the suction side of this pump, boiled lye being drawn out and circulated while the carbonated lye would be drawn in by the partial vacuum created. The gas holder 14 can also lie-dispensed with and the gas drawn direct by the compressor fi'ecting the liquefaction of the gas for commercial use.

In this case the boiler'il, heaters 9' and 10 and coolers l1 and 12, are under reduced pressure produced by suction of the lye pump 7 and the gas compressor 17. The water of condensation and make up water from the coolers instead of passing to the decarbonated lye tank 6 is utilized for diluting the carbonated lye, and may be added at 10.

The preferred form of boiler is shown at Fig. 3 in cross-section. It comprises a square or other vessel, 18, with a number of superimposed trays 19. These trays, 19, are of a size to allow the carbonated lye passing successively over them to decompose. They are arranged as shown, so that the final boiling takes place at the bottom of the vessel. In the case shown, the heating is effected by direct heat from the furnace 20,

but other heating device may be substituted for or used in addition to the furnace 20.

These drawings are by way of example only as the process may be efiected. by various forms of plants, as'will be readily understood.

a I claim:

1. The process of manufacturing carbonic acid gas, which consists in carbonating' an aqueous solution of a carbonate of an alkaline metal, diluting the same, and then-decarbonating the resulting solution.

2. The process of manufacturing carbonic acid gas, which consists in carbonating an aqueous solution of a carbonate of an alkaline metal, diluting the same, and then decarbonating the resulting solution under reduced pressure. p

3. The process of manufacturing carbonic acid gas, which consists incarbonating an aqueous solution of a carbonate'of an alkaline metal, varying the strengthof the same between the decomposer andfabsorber, and

'eifecting the decomposition offth'e resulting solution under decreased qpressure in the v decomposer.

4:. The process of producing'carbonic acid gas, which consists in carbonating to the saturation point an aqueous solut1on of a carbonate of potassium, diluting the same, and decarbonating the resulting solution under a decreased pressure.

. lutin the solution thus carbonated, and then decar onating the same under reduced pressure.

In testimony'whereof, I, ALBERT EDGAR KNOWLES, have signed my name to this specification in the presence of two subscribingwitnesses, this 17th day of July 1907.

ALBERT EDGAR KNOWLES.

Witnesses:

' F. G. BRE'rrELL,

ERNEST HARKER. 

